1. Field of the Invention
The invention relates to high-density optical data storage systems. More particularly, it relates to improvements in Surface-Enhanced Raman Optical Data Storage (SERODS) systems that make possible the reading and writing of large amounts of surface-enhanced Raman scattering (SERS) data at very fast rates.
2. Background Information
Surface-Enhanced Raman Optical Data Storage (SERODS) systems based on the surface-enhanced Raman scattering (SERS) effect are a recent development in the field of high-density optical data storage. See, for example, the inventor""s U.S. Pat. No. 4,999,810, Issued Mar. 12, 1991; and his U.S. Pat. No. 5,325,342, Issued Jun. 28, 1994.
In these systems, the information is recorded on some form of SERODS medium. This is usually a two-dimensional (2-D) SERODS disk or a three-dimensional (3-D) stack of two-dimensional SERODS disks. Monolithic multilayer 3-D optical disks, which could contain SERS data, are also known. A single SERODS disk usually comprises at least a flat, optically transparent substrate having two opposed faces. A SERS-active coating is placed on at least one of the faces. A writing process such as the one described in the above patents embeds information (data) in the SERS-active coating. The embedded SERS data is termed microspots, although their size could be in the sub-micron or nanometer range, and be referred to as xe2x80x9cnanospotsxe2x80x9d. While such systems have demonstrated excellent high-density optical data storage capability, it is desirable to increase their reading speed and data transfer rate significantly.
The present invention provides means for ultrafast transfer of large amounts of data in both the writing and reading processes in SERODS systems. This new capability is called parallel signal transfer, or PST. The PST enhancement to SERODS systems will be useful for applications that require huge memory capacity with ultrafast parallel data writing, reading and transfer.
The SERS technology is based on the principle that the enhanced Raman light-emitting properties of certain molecules (usually dye molecules) embedded in an optical medium can be altered at the molecular level to store information. Normal Raman signals are generally very weak and cannot be easily detected. The SERS effect, however, can enhance the Raman signal up to 108 times, and make Raman detection possible for optical data reading with the SERODS technology. The basic principles of the SERS effect have been recently discussed. See, for example, T. Vo-Dinh, xe2x80x9cSurface-Enhanced Raman Scatteringxe2x80x9d, in Photonic Probes of Surfaces, P. Halevi, Ed., Elsevier, New York (1995).
With the SERODS technology, the molecular interactions between the optical-layer molecules and the substrate are modified by the writing laser, changing their SERS-emitting properties so that they are encoded to store information as bits. The intensity of the SERS signal of a chemical deposited on a substrate depends strongly on its molecular interaction with the substrate microenvironment adjacent to it. The basic operating principle of SERODS is to alter this chemical/substrate interaction at the molecular level in a laser xe2x80x9cwrite-onxe2x80x9d process, and to monitor the change in the SERS signal intensity of molecules in the optical layer in a xe2x80x9cread-outxe2x80x9d process that uses laser irradiation or other means.
The embedded information is recovered from the recorded medium by detecting the changes in the SERS signal from the altered molecules by a photodetector that tracks the changes in the amplitude and spatial distribution of the SERS signal from different microregions on the disk.
In the conventional SERODS systems, a scanning device such as a photodetector is used for sequential data reading. However, the reading speed of such SERODS systems is limited by the scanning speed of the mechanical device, i.e., the disk rotation speed and the disk scanning system.
In contrast, the present invention is a system for writing or reading SERS data by using a two-dimensional writing or reading process called parallel signal transfer, or PST. This is an improvement to the present SERODS systems which utilize a scanning process where the SERS signal of each written bit is read sequentially one at a time. The PST reading process involves two-dimensional data reading with simultaneous detection of all information bits written on one entire two-dimensional (2-D) SERODS disk.
The following example illustrates the advantages of the PST improvement. With a sequential scanning SERODS system, a reading time, or SERS signal integration time of 0.1 xcexcsec per data produces a reading speed of 10 Mbit/sec. On the other hand, a SERODS system with PST would transfer 106 bits simultaneously using a longer integration time of 1 msec.
This is a reading speed of 1 Gigabit/sec, which is 100 times faster than the conventional sequential scanning system.
1. Emerging Optical Storage technologies, Chapter 3, Loyola University, 4 pages; HTML published February 1996 at http://itri.loyola.edu/opto/c3_s5.htm.
2. T. Vo-Dinh, Surface Enhanced RAMAN Optical Data Storage System, U.S. Pat. No. 4,999,810, Issued Mar. 12, 1991.
3. T. Vo-Dinh, Surface Enhanced RAMAN Optical Data Storage System, U.S. Pat. No. 5,325,342, Issued Jun. 28, 1994.
4. T. Vo-Dinh, xe2x80x9cPrinciple of SERODS: A New Concept for Optical Data Storagexe2x80x9d, Proc. 1994 Spring Conference on Solid-State Memory Technologies, Pasadena, Calif., May 23-25 (1994), Appendix pages 101-110.
5. T. Vo-Dinh, xe2x80x9cSERODS: Principle of a New Optical Data Storage Systemxe2x80x9d in Optical Data Storage, D. Campell, M. Chen and K. Ogawa, Eds., SPIE Vol. 2338, Bellingham, WA (1994), pp. 148-155.
6. T. Vo-Dinh and D. L. Stokes, xe2x80x9cSurface-Enhanced Raman Optical Data Storage: A New Optical Memory with Three-Dimensional Data Storagexe2x80x9d, Rev. Sci. Instrum., 65(12), (December 1994), pp. 3766-3770.
7. T. Vo-Dinh, xe2x80x9cSurface-Enhanced Raman Scatteringxe2x80x9d, in Photonic Probes of Surfaces, P. Halevi, Ed., Elsevier, New York (1995), pp. 65-95.
8. T. Vo-Dinh, xe2x80x9cSurface-Enhanced Raman Spectroscopy Using Metallic Nanostructuresxe2x80x9d, Trends in Analytical Chemistry, 17(8and9), (1998), pp. 557-582.
It is a first object of the invention to provide improved writing and reading systems for two-dimensional single or stacked SERODS disks and for three-dimensional SERODS media.
A second object of the invention is to provide data reading speeds (transfer rates) in SERODS writing and reading systems in the Megabit and Gigabit ranges.
A parallel signal transfer system (PSTS) for writing a surface-enhanced Raman optical data storage (SERODS) medium has: a pulsed laser providing optical light pulses to the SERODS medium, the laser adapted to produce two-dimensional surface-enhanced Raman scattering (SERS) microspots in the SERODS medium; a beam splitter for splitting the optical light pulses into first and second pulsed beams; a cylindrical mirror system positioned in the first pulsed beam path, the cylindrical mirror system adapted for spreading the first pulsed beam into a 2-D excitation plane; an optical delay positioned in the second pulsed beam path, the optical delay adapted for producing pulse overlap with the first pulsed beam for two-photon excitation in the SERODS medium; a two-dimensional detector receiving a two-dimensional SERS optical light image signal of the microspots from the SERODS medium, the two-dimensional detector adapted for producing a 2-D image of the 2-D SERS optical light image signal; and a holographic notch filter positioned between the SERODS medium and the two-dimensional detector, the holographic notch filter rejecting the Raleigh scatter from the two-dimensional SERS optical light image signal.
Another parallel signal transfer system (PSTS) for writing a surface-enhanced Raman optical data storage (SERODS) medium has: a first pulsed laser providing a first pulsed optical light beam to the SERODS medium, the laser adapted to produce two-dimensional surface-enhanced Raman scattering (SERS) microspots in the SERODS medium; a cylindrical mirror system positioned in the first pulsed optical light beam path, the cylindrical mirror system adapted for spreading the first pulsed beam into a 2-D excitation plane; a second pulsed laser providing a second pulsed optical light beam to the SERODS medium, the laser adapted to produce two-dimensional surface-enhanced Raman scattering (SERS) microspots in the SERODS medium; an optical delay positioned in the second pulsed beam path, the optical delay adapted for producing pulse overlap with the first pulsed beam for two-photon excitation in the SERODS medium; a two-dimensional detector receiving a two-dimensional SERS optical light image signal of the microspots from the SERODS medium, the two-dimensional detector adapted for producing a 2-D image of the 2-D SERS optical light image signal; and a holographic notch filter positioned between the SERODS medium and the two-dimensional detector, the holographic notch filter rejecting the Raleigh scatter from the two-dimensional SERS optical light image signal.
Another parallel signal transfer system (PSTS) for writing a surface-enhanced Raman optical data storage (SERODS) medium has: a laser providing an optical light beam to the SERODS medium, the laser adapted to produce two-dimensional surface-enhanced Raman scattering (SERS) microspots in the SERODS medium; a beam splitter for splitting the optical light beam into first and second optical light beams; a cylindrical mirror system positioned in the first optical light beam path, the cylindrical mirror system adapted for spreading the first optical light beam into a 2-D excitation plane; an acousto-optic modulator positioned in the second optical light beam path, the acousto-optic modulator adapted for deflecting the second optical light beam; an optical delay positioned in the second optical light beam path, the optical delay adapted for producing overlap with the first optical light beam for two-phonton excitation in the SERODS medium; a two-dimensional detector receiving a two-dimensional SERS optical light image signal of the microspots from the SERODS medium, the two-dimensional detector adapted for producing a 2-D image of the 2-D SERS optical light image signal; and a holographic notch filter positioned between the SERODS medium and the two-dimensional detector, the holographic notch filter rejecting the Raleigh scatter from the two-dimensional SERS optical light image signal.
Another parallel signal transfer system (PSTS) for writing a surface-enhanced Raman optical data storage (SERODS) medium has: a laser providing a first optical light beam to the SERODS medium, the laser adapted to produce two-dimensional surface-enhanced Raman scattering (SERS) microspots in the SERODS medium; a cylindrical mirror system positioned in the first optical light beam path, the cylindrical mirror system adapted for spreading the first optical light beam into a 2-D excitation plane; a second laser providing a second optical light beam to the SERODS medium, the laser adapted to produce two-dimensional surface-enhanced Raman scattering (SERS) microspots in the SERODS medium; an acousto-optic modulator positioned in the second optical light beam path, the acousto-optic modulator adapted for deflecting the second optical light beam; an optical delay positioned in the second optical light beam path, the optical delay adapted for producing overlap with the first optical light beam for two-photon excitation in the SERODS medium; a two-dimensional detector receiving a two-dimensional SERS optical light image signal of the microspots from the SERODS medium, the two-dimensional detector adapted for producing a 2-D image of the 2-D SERS optical light image signal; and a holographic notch filter positioned between the SERODS medium and the two-dimensional detector, the holographic notch filter rejecting the Raleigh scatter from the two-dimensional SERS optical light image signal.